He's photographed 11 US presidents, beautiful women ranging from Dame Elizabeth Taylor to Ms Kate Moss, the construction and demolition of the Berlin Wall, the assassination of a Kennedy, the struggle for Civil Rights, the world's greatest rock'n'roll band, as well as the famine in Somalia and the aftermath of Hurricane Katrina. Mr Harry Benson isn't just an extraordinary photographer; he's a one-man history archive, and he's about to mount his first major retrospective in England.

What accounts for his success? Mr Benson is dismissive of his technical skills, in the way that only someone who's supremely confident about them can be, saying, "Cameras are actually quite easy to learn, you've only got eight stops, you've just got to learn to be as quick as you can." However, he repeatedly emphasises the importance of proximity. When asked about those presidential portraits, he says, "I'm trying to get as close to them as I can." When discussing his approach to photojournalism, the same theme emerges: "I don't want to be on the periphery, my main concern is, 'Am I getting to the middle of this?'"

This approach has taken him to the midst of many of the key events of the past half-century. "I was glad I was in Berlin the day it [the wall] went up, but 50 years ago I wasn't thinking of talking to you about it, I was thinking of being paid at the end of the week, and keeping my job." As to how he sets about getting a great shot Mr Benson explains, "There's such emotion going on about you, you're trying to get yourself into a good spot where it makes sense." The images of Dr Martin Luther King Jr, East German bricklayers, and Mr Bobby Kennedy's widow, demonstrate his unrivalled ability to find the best spots.

Mr Benson felt fearful in such situations, but took precautions. "I was very aware of what I was doing if I did dangerous stories, such as the Watts Riots or in the Congo. I usually went alone, because photographers are inclined to get in danger when they're in a pack. I go lightly, with a camera and two lenses; don't weigh myself down. If you have too much equipment you're rattling about and you're not mobile. Being mobile is so important to what I do."

In a career marked by the drama of his subject matter, what's the most shocking thing Mr Benson has ever witnessed? "It's hard to get away from an assassination," he replies, referring to the shooting of Senator Robert F Kennedy on 5 June 1968. "There was somebody that I liked, and he was murdered right in front of me. I was about three yards away when he was shot." The way he tells it, Mr Benson went into professional autopilot: "I had to keep a clear head, and keep working. People were hitting me, other people were being shot around me, there was blood all over the place, it was a terrible scene."

However, Mr Benson's career hasn't been entirely defined by such dark moments. He's also photographed the leading cultural lights of the past half-century, most notably The Beatles. "I was meant to be going to Africa, and then at the last hour I was told I was going to Paris to shoot The Beatles. I wasn't too happy about it because I wasn't a rock'n'roll photographer," he remembers. "But as soon as I heard the music I knew I was on the right story." His photographs didn't just capture the emergence of the world greatest rock'n'roll band, they changed Mr Benson's life. "It meant I was going to America," he says. "I stayed, and I worked for Life magazine and that's what I wanted to do, to work for a good magazine." Fifty years later Mr Benson still lives in New York, and spends winters in Florida's Palm Beach.

Palm Beach is a long way from Glasgow, Scotland's second city, which is where he grew up. First published at 16, with a picture of a roe deer taken at Glasgow's zoo, Mr Benson describes "the wonderful feeling" he got when he saw his shot in Glasgow's Evening Times newspaper. However, like many young men his career was not his focus. "I'm in Glasgow one day, and I look in the window of a men's shop and here's a model wearing the new Robert Mitchum look, which was a jacket with big shoulders. I pawned my camera so I could buy that jacket," he admits. "I wanted to show off to girls."

It wasn't until Mr Benson completed his military service, and spent time working as a wedding photographer, that he broke through with a job for the Daily Sketch newspaper. Rehearsing his career, however, does nothing to explain his remarkable drive, which he encapsulates when he says, "I always tried to be the first in and the last out." His ambition, it seems, goes back to the way he was treated by the Scottish education system. "It was based on a lot of refusals," he says. "On having to leave school at 13 - you had to pass an exam but I was never able to do anything that bored me. So I had to leave school early, and I got a job being a messenger boy, and I'd come home and the other boys and girls were rehearsing for their school play. I was angry at a very early age; photography was a way out."

I was very aware of what I was doing if I did dangerous stories. I usually went alone, because photographers tend to get into danger if they are in a pack

Looking back over the momentous, and horrifying, events for which Mr Benson has borne witness, does he feel gloomy? "It worries me, it troubles me. But I get over it because there's another job. I'm very optimistic. I think we're living in one of the best times ever. I grew up in the war with Germany, then we had Russia with nuclear weapons all around. There's nothing we can't handle." And from a photographic perspective, given that he's had to review his entire career for the new show, what does he conclude makes a great shot? "A good photograph cannot be copied, it cannot happen again, it's a glimpse and gone forever. It can't be touched."

Harry Benson: 50 Years Behind the Lens runs from 14 to 15 February at Mallett, 37 Dover Street, London. mallettantiques.com